NameVirtualHost 192.168.1.1:80

<VirtualHost 192.168.1.1:80>
  ProxyPass / http://192.168.1.80/
  ProxyPassReverse / http://192.168.1.80/
  ServerName some.virtual.host

  ErrorLog /var/log/apache/proxy_error_log
  CustomLog /var/log/apache/proxy_access_log combined
</VirtualHost>

<VirtualHost 192.168.1.1:80>
  ProxyPass / http://192.168.1.81/
  ProxyPassReverse / http://192.168.1.81/
  ServerName some.other.vhost

  ErrorLog /var/log/apache/proxy_error_log
  CustomLog /var/log/apache/proxy_access_log combined
</VirtualHost>

<VirtualHost 192.168.1.1:80>
  ServerName yet.another.vhost

  DocumentRoot /var/www/some/vhost.rootdir
  ErrorLog /var/log/apache/proxy_error_log
  CustomLog /var/log/apache/proxy_access_log combined
</VirtualHost>